A variety of diagnostic devices have been developed for the detection of an analyte of interest in a sample. In those devices in which sample collection and testing functions are non-linked, the transfer of collected sample to testing apparatus introduces a potential source of error. In those devices in which sample collection and testing functions are linked, the devices are dedicated in their entirety to the detection of a particular analyte and are not easily adaptable to a wide range of analyte detection.
With respect to mammalian systems (e.g. humans), samples amenable to analysis using the testing device of the present invention include biological fluids (e.g. blood, urine, semen, saliva, etc.) or excrements. Such biological fluids can carry a variety of analytes, the presence of which can be diagnostic for a particular disease state. The application of the subject invention to the detection of disease states in humans is of primary importance. However, in addition to use in the context of the diagnosis of serious disease states, the present invention is also useful in a variety of other contexts. Applications in connection with the analysis of microbes, plants, animals, food and water are all anticipated.
For example, ground water samples can be analysed for the presence of contaminants such as atrazine. Food, such as ground beef, can be analysed for the presence of contamination by bacteria such as E. coli. In the plant kingdom, the present invention can be applied to the analysis of, for example, pollen, spores and plant vascular fluids. Generally speaking, the only requirement for detection using the device and method of the present invention is that the analyte of interest should be soluble or suspendible in an aqueous solution.
The present invention relates to a device which is useful inter alia for the detection of any aqueous soluble or suspendible analyte which is detectable, for example, on the basis of immunological and/or chemical properties. An example of an analyte detected by its immunological properties includes, but is not limited to, an immune interacting molecule such as an antigen, hapten, immunoglobulin or T-cell derived antigen binding molecule. An example of an analyte detected by chemical properties includes an enzyme, catalyst or ligand. Thus, in detection of occult gastrointestinal bleeding as a screen for colo-rectal cancer, using the faecal occult blood (FOB) test, the device of the present invention can be adapted to either guaiac-based testing, or immunological testing. The preferred format for immunological testing is immunochromatography. This format is described generally in U.S. Pat. Nos. 5,591,645 and 5,622,871, the disclosures of which are incorporated herein by reference.
Prior to discussing the invention in greater detail, a brief review of the immunochromatography process will be provided to establish certain principles. To detect an analyte of interest by immunochromatography, two binding reagents which bind specifically and non-competitively to the analyte of interest may be employed. A first specific binding reagent is labelled and is free to migrate. When introduced to a sample to be tested for the presence of the analyte of interest, the first specific binding reagent binds to the analyte of interest, if present. The second specific binding reagent is immobilized in a detection zone on a liquid-conductive solid phase material, the detection zone being remote and downstream from the location of initial contact between the first binding reagent and the analyte of interest. A solvent front carrying the mobile first specific binding reagent complexed with analyte of interest (if present) migrates along the liquid-conductive solid phase material through the detection zone. If analyte is present in the sample, the immobilised second specific binding reagent binds the analyte thereby forming an immobilised sandwich complex comprising the first specific binding reagent (which is labelled), the analyte of interest, and the second specific binding reagent (which is immobilised). Detection of the label immobilised in the detection zone is indicative of the presence of analyte of interest in the sample. In most embodiments, the first and second specific binding reagents are either polyclonal or monoclonal antibodies.
Many diagnostic tests and assays involve the use of samples collected in the field and then either tested immediately, or returned to a central facility for later test development. Such samples may include blood, serum, saliva, milk, faeces, urine or other materials of biological origin, or samples collected from the environment, such as water for analysis for nutrients or contamination.
For example, in the practice of medicine, one or more blood samples may be drawn from a patient in the physician's office and then sent to a pathology laboratory for subsequent testing for one or more analytes. Typically the blood is drawn by venipuncture, using an especially designed needle and blood collection tube (e.g. Vacutainer, Becton Dickinson). The collection of the blood by venipuncture requires trained personnel, the provision of suitable facilities and equipment, refrigerated transport and storage facilities, and finally means for accurate sampling, treatment (e.g. serum or plasma separation) and dispensing of the blood/plasma/serum into the test or assay equipment. In many cases the blood is only used for one test and, if an effective collection means were available. the blood from a finger prick would be sufficient.
Recently, there has been a marked increase in the use of “Point of Care” (POC) testing, using rapid, self-developing test systems packaged in simple, single-use, disposable test devices. Such POC tests include assays for glucose monitoring, pregnancy and infections such as Streptococcal infection of the throat and Chlamydia infection of the genital tract. Many of these tests, however, introduce a limitation that the test must be conducted immediately at the test site, as the tests have been designed such that the addition of the sample initiates the test. In addition, these tests generally do not incorporate a sample collection system, but rely on the sample being obtained at the time of testing, or else being presented in a separate collection vessel, such as a Vacutainer, as described above.
For many test systems, it is desirable for the sample to be tested to be collected at one site for subsequent test development at another site. In such instances, it is desirable to have a simple, inexpensive and safe means of delivering this testing option, preferably by means of an integral collection and testing system.
Ideally, the prerequisites for such an integrated collection and test system would include:                generic design, that is, one basic format to suit all test applications;        simple, accurate and representative sampling, requiring minimal skills and equipment to collect the sample;        safe, stable, and inexpensive storage of the sample;        effective reconstitution and/or displacement of the sample to the testing means for development of the test; and        cost-effective delivery of the test result.        
It is an object of the present invention to provide a test format that meets these requirements and is suited for the delivery of samples for either immediate or later testing.